Mobile stations such as those for use with the GSM and UMTS standards are required to provide unique identities and other information stored in a SIM card (which is usually contained within the mobile station) in order to access the network. The protocols used in such networks are designed to provide functions such as subscription checking and authentication. This ensures that a mobile station should be permitted access to the network (for example so that the correct person can be billed for usage of the network) and also provides a degree of privacy using encryption techniques for the data (voice or otherwise) transferred during the call.
Presently, although the hardware forming the mobile station (for example a mobile telephone or cell phone) contains a unique identity, it is the information contained in the SIM which allows the mobile station to gain access to the network. Thus a user may change mobile phones and generally speaking, as long as the SIM is transferred from the old phone to the new phone, network access will still be permitted. This arrangement has clear commercial advantages for a user and furthermore allows facilities such as SIM card roaming to be provided by network operators and mobile phone providers.
However, a consequence of the arrangements permitting authentication, information and mobile subscriber identity information being held in the SIM card is that a mobile station is usually unable to gain access to the network without a SIM card. Whilst this may appear desirable to prevent fraud, it is undesirable when it is wished to make a call, for example, to the emergency services. In this situation, it is desirable to allow a call to be set up with the minimum of restrictions. Therefore, it is desirable to allow a call to be set up using a mobile station into which a SIM card has not been installed.
This has been achieved for the GSM standard by providing a special protocol which allows a mobile station to be “authenticated” to the network without using information which would normally be carried on the SIM.
However, the use of special procedures incurs costs for network operators and mobile telephone suppliers. This cost is incurred even though emergency calls are relatively rare and are not revenue generating. Thus there is a desire to provide a low cost solution to the need for the set up of emergency calls using a mobile station which does not have a SIM card.
In the context of this application, the term “authentication” is used more broadly than the simple exchange of authentication keys. This term is used to describe any steps which permit a mobile station to gain communicative access to a cellular wireless communications network.